Project RAINBOW facts for kids
Project RAINBOW was a secret plan by the CIA. Its goal was to make the Lockheed U-2 spy plane harder for Soviet radars to see. This would help the U-2 fly over the Soviet Union without being caught. Even with these efforts, the Soviets still managed to track the U-2 flights.
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Early Spy Flights
The U-2 plane was built by Lockheed Aircraft for the CIA. It was meant to fly very high to take pictures over the Soviet Union. The project leader, Richard M. Bissell, told President Dwight Eisenhower the plane would be invisible to radar at 70,000 ft or 21,000 m (about 21 kilometers) high.
However, the first flights in July 1956 were actually seen by radar. On July 5, a radar system detected a U-2 flying near Smolensk, heading for Moscow. The radar operators even guessed its height was twenty kilometers (66,000 feet). Experts at the time did not believe a plane could fly so high. No missiles were launched because the right defense systems were not in place.
In August, Bissell gathered experts to solve the radar problem. This group included Edwin H. Land, who started Polaroid, physicist Edward Mills Purcell, and Clarence L. "Kelly" Johnson from Lockheed's special Skunk Works team.
The group started working on ways to make the U-2 less visible to radar. They even went to Lincoln Laboratory to get more radar experts. This team worked secretly to find ways to reduce the U-2's radar cross-section. They also worked with Lockheed and military bases to test U-2s in flight.
Lockheed also had its own team working on these secret radar-hiding methods.
How to Hide a Plane: Anti-Radar Tricks
The radar cross-section (RCS) of an object shows how much radar energy it reflects. Think of it like how big a target it appears to radar. A smaller RCS means it's harder to spot. The RCS depends on the object's size, shape, and what it's made of. It also changes with the type of radar waves used. Since different radars use different waves, many tricks were needed to protect the U-2.
Every part of the plane, like the body, tail, wings, and engine openings, could reflect radar. The anti-radar methods they tried fell into two main groups:
- Absorbing the radar energy.
- Creating reflections that would cancel out the plane's own reflections.
Wallpaper: Absorbing Radar Waves
One idea was to put a special material on the U-2's body. This material was called "Wallpaper." It was like a pattern of wires printed on a flexible sheet. This sheet was then glued to a honeycomb structure, which was then put on the plane. It was designed to work against higher-frequency radars.
At first, Wallpaper covered the top and bottom of the plane. But it trapped too much heat inside. So, they only put it on the bottom half of the plane.
Sadly, this heat problem caused a serious accident. On April 2, 1957, pilot Robert Sieker was testing a U-2 with Wallpaper. The engine stalled because of the heat. Sieker lost consciousness and the plane spun out of control. He managed to bail out, but it was too late, and he died.
Trapeze: Wires on the Wings
To reduce reflections from the edges of the wings, they added wires. These wires ran parallel to the front and back edges of the wings. Fiberglass poles were attached to the wingtips to hold the wires in place. Other wires ran from the nose to the wing tanks and from the wing tanks to the plane's body. The horizontal tail part of the plane was treated similarly.
Wires also ran diagonally from the nose to the wing tanks to protect the engine openings. This whole setup was called "Trapeze."
Wires: Strings on the Body
To reduce reflections from the plane's body and vertical tail, they strung wires horizontally. These wires went from the nose to the tail and across the vertical tail. Small magnetic beads were put on the wires to help them work against specific radar frequencies. This simple method was just called "Wires."
The Price of Stealth
The "Wallpaper" caused overheating, which led to a tragic accident. The "Wires" and "Trapeze" additions also caused problems. They made the U-2 fly 5,000 feet (1,500 m) lower and reduced its flying range by 20%. Pilots did not like these changes. One pilot even said the plane looked like it was "wired like a guitar."
Flights with the "Dirty Bird"
On May 6, 1957, Bissell told President Eisenhower about the progress. He said that most flights would go "undetected." In July, the first "dirty bird" (a U-2 with these radar-hiding features) was ready for missions. The first mission with a "Covered Wagon," as they were also called, happened on July 21, 1957.
In total, nine flights were made with these specially treated planes. By May 1958, it was clear that the system was not working well. So, they stopped using it.
What Came Next
By late 1957, it was clear that the radar-hiding tricks only helped a little. Bissell and his science team knew a new plane was needed. They hoped that by designing anti-radar features from the very beginning, the next plane would truly avoid detection.
Key Lessons Learned
Bissell and his Air Force helper, Col. Jack Gibbs, talked with plane builders and scientists. They wanted to understand what materials and designs would work best. On December 4, 1957, Bissell held a meeting where they summarized what they had learned:
- Engines and other metal parts inside the plane needed to be shielded.
- Some parts of the plane's structure could not be shielded. These parts would need to be made clear to radar, using plastic and no metal.
- For protection against certain types of radars (S-band and X-band), the outside of the plane needed to be shaped to reflect radar energy away from the radar unit.
- To reduce reflections, exposed edges of the plane needed to be "softened" so that radar waves would change gradually as they hit the plane.
Project GUSTO: The Next Step
Many people knew about Project RAINBOW. To keep the follow-up work even more secret, they started a new project called "GUSTO." Only those who absolutely needed to know were allowed to work on it. The ideas from Project GUSTO eventually led to the creation of the Lockheed A-12 OXCART, another famous spy plane.
